Chemical process



added catalysts.

, 51, 2,926,3 1 CHEMICALPROCESSW mas-Hm; stem, and Amara-'11; Manage,Coulsdon, England, assignors to The Distillers Coma l m ts? nb wfla lBritish .company Application Ma -7,1957;se rnNo.6s7,s73-

Claims priority, application Great Britain May 22, 1956 scl ims -rciszeosss I 1 invention relates improvements in a processfor lthe productionof C -C acids, .p'articularly iaceticzacid by theliquid-phaseoxidationwith molecularoxyg'enof .substantially paraflinic hydrocarbonscontaining 4-8 car- ,bon. atoms.

The liquid. phaseoxidation-of low' molecular weight parafiins to producelower aliphatic acids is well known,

Suitable feedstocks include .C to C paraifins, obtained for example .bythe-distillation 'of crudespetroleum, and

theseare contacted with molecularzsoxygen at elevated temperatures andpressures in the presence or absence of The acids are suitably recoveredfrom United States Patent the. oxidate by distillation. In one process,described in the British patent specification No. 743,990, theoxidate,

.or the aqueous phase from the'oxidate, is distilled to sep- ..laratethe materials. boiling in'.'the-- presen'ce of water below 99 C.-,hereinafter-termed light ends)- before recovering the C we, acidsfrom'the-oxidate,and the light ends..aresubmitted to further oxidation,preferably with fresh hydrocarbon feed.

In the oxidation process as usu'ally described, using air oroxygen-enriched air as oxidising agent, it is found I that, owing to thehigh volatility of the hydrocarbons, ap-

preciable quantities of hydrocarbons (accompanied by some low-,boilin'gpartial oxidation products, e.g'. acetaldehyde) leave the apparatus inthe stream'of nitrogenous waste-gas from the oxidation even if this iscooled in conventional water-cooled condensers -'to about 30 C.,

be recycled to the oxidation stage, where they are oxidised to givefurther yields of acids. Another method proposed for the recovery ofthese organic materials is to condense them-by cooling the waste-gas toa sufficiently low temperature (below 0 0.) and then to recycle the ;condens ate direct to theoxidation; It is found in' practice, however,that cooling in this way leads to theseparation of ice andlor othersolid material which causes blockages in the cooling systemandrenders.the.operation of such a system technically diflicult orimpossible.

tic acid, comprises oxidising at an elevated temperature and thisresults 'in'a'lower yield of acids per unit weight ..;of.=hydrocarbonfed. It' has been proposed to remove thisorganic material fromthewaste-gas, for example by wscrubbing the waste-gas '(usuallyunderpressure) with ahigh-boili ngoil atatmospheric temperature in asuitable absorber. Inorder'to recoverth is organic material, itmustbethenfstripped from mean 'with'steam or by distillation, usually ata pressure lower than' that used in the absorber; These recoveredorganic materialsican then and C. derived from petroleum,

2,926,191 Patented Feb. 23, 1 960 "ice with molecular oxygen a paraflinhydrocarbon of 4 to 8 carbon atoms or a mixture thereof in the liquidphase to produce lower aliphatic acids of 1 to 4 carbon atoms,

- distilling the primary oxidation product 'to separate as light endsthe materials boiling in thepresence of water below 99 C., contacting ata low temperature the oxidation waste-gases with the light ends wherebyorganic materials from the waste gas are condensed, and thereafteroxidising the light ends together with the condensed material at anelevated temperature in the liquid phase l with molecular oxygen toproduce additional quantities of lower aliphatic acids. In a preferredembodiment'of the invention, the oxidation waste gases are first cooledto about 30 C. to condense out part of the volatile organic materialswhich are recycled to the oxidation stage, and the waste gases are thencontacted with the lightends at a low temperature whereby furtherorganic materials are condensed, the light ends with the'condensedmaterial then being subiected to further oxidation.

'It has been discovered that, in the presence of these vlight ends,*thedegree of cooling required'to ensure that substantially all of theorganic materials are condensed,

does not result in the deposition of ice or; other solid material. Therecovery is aided by working at or near the reaction pressure of theoxidation. The recovered organic material soobtained admixed with or insolution in light ends may be recycled directly to the main oxidation,or

may be oxidised separately.

'In. order to'obtain optimum recovery of the organic materials, theoxidation waste-gases are contacted with the light ends at-a temperaturebetween 1 and --50 C. It is preferred to use temperatures between .-10and e-40. C. The cooling required may be produced by any known method,e.g. by heat exchanging with chilled brine or with a low-boilingrefrigerant liquid, e.g. ammonia or methyl chloride. The light endsmaybe precooled before contactingwith the waste-gas, or the cooling maybeappliedto the contacting vessel, or both may be cooled. In ourpreferred method, the waste-gas, after removal of organic materials bythey process of the invention, is expanded adiabatically,,for instancein a heat engine, thereby furnishing, by means of suitable heat ex--changers at least part of the cooling necessary for the process.' p IThe process may be varied by cooling the waste-gas .in the presence oflight ends containing in solution filtered liquid residues (as definedbelow), the organic 'material so recovered being then recycled to theoxidation with the light ends and dissolved residues. These residues.are the materials formed in the oxidation having boiling points aboveabout 140 C. which have been subjected to filtration. H a

As, starting material for this process it is, preferred to use aparafiinic hydrocarbon fraction of a boilingrange not exceeding about100 C. As an example of a suitable starting material may be mentioned aC to C paraffinic hydrocarbon fraction boiling between about 15 Theprocess of the invention is further illustrated by the followingexample:

Example The oxidation reactor and its ancillary equipment are showndiagrammatically in the accompanying drawing in which the reactor 1 hastwo air feed points 2 at the base and about the mid-point. Freshhydrocarbon was introduced continuously by line 3 via pump 4. Thereactor was run full, and a mixture of gaseous and liquid reactionproducts passed out from the reactor by line 5. The liquid products wereseparated in a separator 6 and returned directly to the bottom of theoxidation tower by line 7. The hot vapour/waste-gas mixture from theSeparator 6 was cooled in a cooler 8, and the liquid condensateseparated in the separator 9, and fed back into the main liquid recyclevia preheater 10. Aqueous reaction product was continuously withdrawnfrom the system via the cooled separator 11, and reduced to atmosphericpressure through the valve 12. Any separated hydrocarbon layer from theseparator 11, returned to the reactor with the rest of the liquidrecycle via line 7. The aqueous product from 11 was fed to a continuousstill '13 where the light ends were taken off at the head and passed toan intermediate storage vessel 14, the kettle product consisting ofacids, water and residues. The kettle product from the still 13 waspassed to a second continuous still 21, where the C -C acids and waterwere taken off at the head through line 22 to a storage vessel 23, andthe residues were taken off from the kettle through line 24. The formic,acetic,

propionic and butyric acids were recovered from the product in 23 byfractional distillations. The residues were cooled to below 30 andfiltered 25 from the separated solid (largely succinic acid). The liquidresidues from 25 were then pumped back to the oxidation,

' but for part of the run this was done by feeding to the storage vessel14 via line 26 and mixing with the light ends.

The waste-gas containing organic material, still under reactionpressure, passed from the separator. 9 through line 20 into the base ofa jacketed packed tower 17 situated at a height several feet above theoxidation tower, and cooled to about +18 C. The light ends from storage14 were transferred by pump 15 to a cooler 16 under the reactionpressure, where they were cooled to an average temperature of 18 C. andthen passed to the top of tower 17. In the tower 17 the waste-gas wasbrought into intimate contact with the cooled light ends. The waste-gasfrom which most of the organics had been removed passed out of the top17, and was vented to atmosphere through valve 18. The solution ofrecovered organic material in light ends returned by gravity to thereaction system by line 19,- and joining in with the major liquidrecycle and hydrocarbon feed to the reactor. i

The feed to the oxidation was a cut from a Middle East petroleum, with aboiling range of approximately 30-70" C., and consisting mainly ofparafiinic hydrocarbons. The oxidation was carried out in the liquidphase at a temperature of 175 C. and at 630 lbs./sq. inch, with air asthe oxidising agent; no catalyst was added. The waste-gas from theoxidation contained 05% oxygen.

A continuous oxidation carried out in this way for a total period of 196hours gave the following yields of acids, expressed as parts by weightper 100 parts by Weight of fresh hydrocarbon fed through line 3; formicacid 14.6, acetic acid 67.5, propionic acid 9.4, butyric acid 1.65;total 93.25 parts. 1

By way of comparison with the above example,"whcn .thecorrespondingprocess was carried out, with recycle of both light ends and residues tothe oxidation, but 0 with the waste-gas from separator 9 vented toatmosphere without treating in accordance with this invention, the yieldof acids obtainedwas much reduced, being as follows: formic acid 11.3,acetic acid 48.1, propionic acid 2.8, butyric acid 0.7; total 62.9 partsper parts of hydrocarbon fed.

We claim:

1. The process for the production of lower aliphatic acids whichcomprises oxidising at an elevated temperature with molecular oxygen aparaffin hydrocarbon of 4 to 8 carbon atoms in the liquid phase toproduce lower aliphatic acids of -1 to 4 carbon atoms and oxidationwaste gases containing recoverable organic mater ial-separating theprimary oxidation product from the oxidation waste gases, distilling theprimary oxidation product to separate as light ends the material boilinginthe presence of water below 99 C.-, contacting at a temperature of 1to 50 C. said oxidation waste gases with the light ends whereby organicmaterials from the waste gases are condensed, and thereafter oxidisingthe light ends. together with the condensed material at an elevatedtemperature in the liquid phase with molecular oxygen to produceadditional quantities of lower aliphatic acids.

.2. The process as claimed in claim 1 wherein the oxidation waste gasesare cooled to about 30 C. to condense out part of the volatile organicmaterials, said part being recycled to the oxidation stage, before beingcontacted with the light ends at a low temperature.

3. The process. as claimed in claim 1 wherein the oxidation waste gasesare contacted with the light ends ata temperature between 10 and 40 C.

4. The process as claimed in claim 1 wherein the light ends containingcondensed material from the oxidation waste gases are recycled to theoxidation stage.

5. The process as claimed in claim 1' wherein the oxidation Wastegasesare contacted with the light ends at the pressure used in the oxidationreaction.

6. The process as claimed in claim 5 wherein the waste gas after beingcontacted with the light ends is expanded adiabatically to furnish atleast part of the cooling necessary for the process.

7. Theprocess as claimed in claim 1 wherein the oxidationwaste gases arecontacted with light ends containing dissolved, filtered, liquidoxidation residues.

8. A process which comprises continuously oxidizing with molecularoxygen a parafiin hydrocarbon boiling at not over 100 C., producing amixture of aliphatic acids of 1 to 4 carbon atoms, light ends, andoxidation waste gases containing organic matter, said light ends boilingin the presence of water below 99 C., distilling the mixture andcollecting acids, light ends and gaseous products separately, coolingsuch light ends to a temperature between about '-1 to --50.C., washingsaid gaseous products with such cooled light, ends to form a solution ofsubstances other than waste gas and continuously recycling and oxidizingsuch solution with-fresh hydrocarbon to produce further amounts ofacids, light ends and gaseous products.

FOREIGN PATENTS 743,990 Great Britain Ian. 25, 1956

1. THE PROCESS FOR THE PRODUCTION OF LOWER ALIPHATIC ACIDS WHICHCOMPRISES OXIDISING AT AN ELEVATED TEMPERATURE WITH MOLECULAR OXYGEN APARAFFIN HYDROCARBON OF 4 TO 8 CARBON ATOMS IN THE LIQUID PHASE TOPRODUCE LOWER ALIPHATIC ACIDS OF 1 TO 4 CARBON ATOMS AND OXIDATION WASTEGASES CONTAINING RECOVERABLE ORGANIC MATERIAL SEPARATING THE PRIMARYOXIDATION PRODUCT FROM THE OXIDATION WASTE GASES, DISTILLING OXIDATIONPRODUCT TO SEPARATE AS LIGHT ENDS THE MATERIAL BOILING IN THE PRESENCEOF WATER BELOW 99*C., CONTACTING AT A TEMPERATURE OF -1 TO -50*C. SAIDOXIDATION WASTE GASES ARE ENDS WHEREBY ORGANIC MATERIALS FROM THE WASTEGASES ARE CONDENSED, AND THEREAFTER OXIDISING THE LIGHT ENDS TOGETHERWITH THE CONDENSED MATERIAL AT AN ELEVATED TEMPERATURE IN THE LIQUIDPHASE WITH MOLECULAR OXYGEN YO PRODUCE ADDITIONAL QUANTITIES OF LOWERALIPHATIC ACIDS.